1. The Field of the Invention
The present invention is in the field of dental trays used to provide a desired dental treatment to a person's teeth. More particularly, the invention relates to pre-shaped, non-custom dental trays that are useful in applying a dental treatment composition to a person's teeth (e.g., a dental bleaching composition).
2. The Relevant Technology
Virtually all people desire white or whiter teeth. To achieve this goal, people either a have veneers placed over their teeth or have their teeth chemically bleached. In the past, patients who desired to have their teeth bleached had to submit to conventional in-office bleaching techniques. The process generally involves: (1) making an alginate impression of the patient's teeth; (2) making a stone cast or model of the impression; (3) vacuum forming a dental tray from the model, usually from a heated sheet of thin ethyl vinyl acetate (EVA) material, and (4) trimming to exclude gingival coverage. This method results in a tray that is soft and flexible, that is customized to very accurately fit over the patient's teeth, and that is therefore very comfortable to wear. However, the process for making a customized tray is time consuming, often taking days or weeks before the customized tray is available to the patient, and the resulting tray is quite expensive.
Because of the time and cost associated with customized trays, less costly alternatives have been developed, but these alternatives have substantial disadvantages in terms of accuracy, effectiveness, and comfort.
One alternative is the so-called “boil and bite” tray. A relatively thick, non-custom preformed tray (similar to a mouth guard) made of EVA or polyethylene or other material is submerged in boiling water. The preformed tray is relatively thick (e.g., >2 mm) to prevent the tray from collapsing on itself and becoming entirely unusable during the heating process. Upon removal from the heated water, the tray is quickly placed inside the patient's mouth. The patient quickly bites down and applies contact pressure to make an impression of the biting surfaces of the user's teeth. One problem with “boil and bite” trays is that they are relatively thick and bulky, which make them more intrusive and less comfortable to wear compared to customized trays. The thickness of large, bulky preformed trays also limits the accuracy with which they can conform to the user's teeth and/or gums and makes the trays more rigid.
To the extent that boil and bite trays made from EVA and like materials are made with thinner walls, such trays are extremely difficult to work with because they tend to shrivel and collapse outside extremely narrow windows of temperature and heating time. For example, if left in a hot water bath too long (i.e., for more than a few seconds) they can quickly become limp and lose their pre-form shape, making it difficult or impossible to conform the tray to the user's teeth. In view of the foregoing, “boil and bite” trays that do not have the tendency to collapse and shrivel when heated generally do not accurately conform to the user's teeth and are bulky and uncomfortable to wear.
Another alternative for teeth bleaching involves non-customized strips of a flexible plastic material coated with a bleaching agent that can be applied to the teeth. Such strips are placed against the teeth by the user to cover the labial surface of the front 6 teeth. Such strips do not readily surround the dental arch, and are rather ineffective in holding the bleaching composition against the teeth. Because the structure of the device is a simple strip that is initially flat, they are awkward to place and may not hold the bleaching agent against the teeth long enough for a single treatment to have the desired effect. Frequent replacement and refitting of the strips is often required. In addition, they treat only the teeth at the front of the dental arch, they provide little or no treatment of the lingual surfaces of the tooth, and they do not provide adequate treatment to the margins between the teeth. Finally, the upper and lower dental arches are typically bleached individually. Trying to place separate strips over the upper and lower dental arches at the same time can be quite difficult.
Another alternative is a dual tray assembly as disclosed in U.S. Pat. No. 5,616,027 to Jacobs et al. The dual tray assembly is composed of an outer tray that supports or carries an inner tray made of a thermoplastic material comprising EVA. In use, the tray assembly is submerged in hot water, whereby the inner tray becomes pliable and moldable and the outer tray remains rigid. The heated assembly is then placed in the mouth of the patient where the inner tray takes an impression of the patient's teeth. Thereafter, the assembly is removed from the patient's mouth and the inner tray is removed from the assembly and trimmed so as to yield a customized tray that is thinner and more comfortable to wear compared to conventional “boil and bite” trays.
In view of the foregoing, there is an ongoing need to develop alternatives that are simpler to use but that result in a comfortable-fitting dental tray in order to promote compliance with a particular treatment regimen.